Exhaust hydrocarbons and odor were reduced in Detroit Diesel Series “71” engines by revising the fuel injector tip design. Five injector tips were investigated which had different volumes of uncontrolled fuel below the injector valve. Results are presented to show that exhaust hydrocarbons and odor can be substantially reduced by minimizing the uncontrolled volume of fuel in the injector tip. The hydrocarbon emissions are attributed to uncontrolled fuel being pushed from the tip by expansion of the fuel at elevated temperatures. This conclusion is supported by test results with fuels having different 10% distillation temperatures.